Re: [Idr] [spring] Comments: Route Origin Community in SR Policy(draft-ietf-spring-segment-routing-policy)
Gyan Mishra <hayabusagsm@gmail.com> Thu, 21 May 2020 19:17 UTC
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From: Gyan Mishra <hayabusagsm@gmail.com>
Date: Thu, 21 May 2020 15:17:42 -0400
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To: Robert Raszuk <robert@raszuk.net>
Cc: "Chengli (Cheng Li)" <c.l@huawei.com>, Fangsheng <fangsheng@huawei.com>, "Ketan Talaulikar (ketant)" <ketant@cisco.com>, SPRING WG <spring@ietf.org>, Yangang <yangang@huawei.com>, "draft-ietf-spring-segment-routing-policy@ietf.org" <draft-ietf-spring-segment-routing-policy@ietf.org>, idr wg <idr@ietf.org>, stefano previdi <stefano@previdi.net>
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Subject: Re: [Idr] [spring] Comments: Route Origin Community in SR Policy(draft-ietf-spring-segment-routing-policy)
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On Wed, May 20, 2020 at 8:59 AM Robert Raszuk <robert@raszuk.net> wrote: > Hi, > > > the node-address is generated by CSG1 > > I don't think CSG1 needs to "generate" anything. Peers which send you > particular policy are well known at CSG1. > > > The process described above will result in a waste of redundant > candidate paths on CSG1, > > Well what you call "waste" I call redundancy. Sure keeping extra paths > requires some cost, but building redundancy in control plane pays off. > Gyan> I agree with Robert that the additional candidate path sent by the RR could be used for redundancy. However, I think the context of SR TE is that each candidate path is a single path option not multiple as the redundancy is provided by different candidate paths. That is the issue I am guessing. > Thx, > R. > > > > > On Wed, May 20, 2020 at 2:32 PM Fangsheng <fangsheng@huawei.com> wrote: > >> Hi Robert, >> >> Take the following picture as an example, I think you can understand our >> problem more easily. >> >> The controller needs to notify the headend CSG1 through BGP SR Policy to >> create a candidate path of SR Policy. This BGP SR Policy route will be >> advertised to CSG1 through RR1 and RR2. >> >> According to the definition in draft, the key of a candidate path is >> <Protocol-Origin, originator, discriminator>, where originator = <ASN, >> node-address>, so a complete candidate path key is <Protocol-Origin, ASN, >> node-address , discriminator>. >> >> However, in this specific example, the node-address is generated by CSG1, >> and because CSG1 receives BGP SR Policy routes from RR1 and RR2, >> respectively, CSG1 will get two different node-addresses. CSG1 thinks that >> it is necessary to create two candidate paths, and the controller does not >> know what the node-address CSG1 will eventually generate. Maybe: >> >> Candidate path 1’ key: <*BGP,RR1’s ASN, RR1’ BGP Router ID, >> discriminator1*> >> >> Candidate path 2’ key: <*BGP,RR2’s ASN, RR2’ BGP Router ID, >> discriminator2*> >> >> The process described above will result in a waste of redundant candidate >> paths on CSG1, >> >> At the same time, when CSG1 needs to announce the SR Policy information >> to the controller through BGP LS, it needs to carry the keys of the >> candidate path in it, and the controller cannot recognize these keys. >> >> >> >> >> >> >> >> To solve these problems, We recommend carrying the Route Origin >> Community (defined in RFC 4360) directly when the controller advertises BGP >> routes. >> >> In this way, the key of the CP is determined by the controller and will >> not change during the advertisement of BGP routes. >> >> >> >> >> >> >> >> >> >> *发件人:* Ketan Talaulikar (ketant) [mailto:ketant@cisco.com] >> *发送时间:* 2020年5月18日 20:00 >> *收件人:* Robert Raszuk <robert@raszuk.net> >> *抄送:* Chengli (Cheng Li) <c.l@huawei.com>; >> draft-ietf-spring-segment-routing-policy@ietf.org; idr wg <idr@ietf.org>; >> SPRING WG <spring@ietf.org>; Fangsheng <fangsheng@huawei.com>; stefano >> previdi <stefano@previdi.net> >> *主题:* RE: [Idr] Comments: Route Origin Community in SR >> Policy(draft-ietf-spring-segment-routing-policy) >> >> >> >> Hi Robert, >> >> >> >> You are right that the “Originator” is not used in BGP best path and is >> just for a tie-breaking logic in SRTE between paths from different >> protocols and controllers. I doubt if there is a functional issue here. >> >> >> >> I thought that Chengli was bringing in some new/different requirement for >> the “Originator” field for some deployment design. I haven’t seen a >> response/clarification from him as yet, and so perhaps I misunderstood him >> in which case we are ok here. >> >> >> >> Thanks, >> >> Ketan >> >> >> >> *From:* Robert Raszuk <robert@raszuk.net> >> *Sent:* 30 April 2020 14:46 >> *To:* Ketan Talaulikar (ketant) <ketant@cisco.com> >> *Cc:* Chengli (Cheng Li) <chengli13@huawei.com>; >> draft-ietf-spring-segment-routing-policy@ietf.org; idr wg <idr@ietf.org>; >> SPRING WG <spring@ietf.org>; Fangsheng <fangsheng@huawei.com>; stefano >> previdi <stefano@previdi.net> >> *Subject:* Re: [Idr] Comments: Route Origin Community in SR >> Policy(draft-ietf-spring-segment-routing-policy) >> >> >> >> Hi Chengli and Ketan, >> >> >> >> Well I think (perhaps to your surprise) the current text is actually >> correct. >> >> >> >> See the overall idea of section 2.4 is not to define the real source of >> the candidate path. That is done in section 2.5 The idea here is to keep >> multiple *paths or versions* of the candidate paths in the local system >> uniquely. >> >> >> >> See if you continue reading section 2.6 demystifies the real objective: >> >> >> >> The tuple <Protocol-Origin, originator, discriminator> uniquely >> >> identifies a candidate path. >> >> >> >> So the real originator is encoded in discriminator and here it just means the peer candidate path was >> >> received from. And if you read on this entire exercise only servers best path selection as described in section 2.9. >> >> >> >> .... the following order until only one valid best path is selected: >> >> >> >> 1. Higher value of Protocol-Origin is selected. >> >> >> >> 2. If specified by configuration, prefer the existing installed >> >> path. >> >> >> >> 3. Lower value of originator is selected. >> >> >> >> 4. Finally, the higher value of discriminator is selected. >> >> >> >> + >> >> The originator allows an operator to have multiple redundant >> >> controllers and still maintain a deterministic behaviour over >> >> which of them are preferred even if they are providing the same >> >> candidate paths for the same SR policies to the headend. >> >> >> >> Thx, >> R. >> >> >> > On Thu, Apr 30, 2020 at 10:46 AM Ketan Talaulikar (ketant) <ketant= >> 40cisco.com@dmarc.ietf.org> wrote: >> > Hi Cheng, >> >> >> >> I assume you are recommending the use of Route Origin Extended Community ( >> https://tools.ietf.org/html/rfc4360#section-5) for conveying the >> “Originator” when the SR Policy update is propagated over eBGP sessions via >> other eBGP/iBGP sessions instead of direct peering with the headend. >> >> >> >> I believe it does address the scenario you describe given that it is >> expected that SR Policy propagation via BGP is happening within a single >> administrative domain even if it comprises of multiple ASes. >> >> >> >> Also copying the IDR WG for inputs since this would likely need to be >> updated in draft-ietf-idr-segment-routing-te-policy. >> >> >> >> Thanks, >> >> Ketan >> >> >> >> *From:* spring <spring-bounces@ietf.org> *On Behalf Of *Chengli (Cheng >> Li) >> *Sent:* 30 April 2020 07:34 >> *To:* draft-ietf-spring-segment-routing-policy@ietf.org >> *Cc:* SPRING WG <spring@ietf.org>; huruizhao <huruizhao@huawei.com>; >> Fangsheng <fangsheng@huawei.com> >> *Subject:* [spring] Comments: Route Origin Community in SR >> Policy(draft-ietf-spring-segment-routing-policy) >> >> >> >> Hi authors, >> >> >> >> In section 2.4 of [draft-ietf-spring-segment-routing-policy-06], >> introduced how the node-address of "Originator of CP(Candidate Path)" is >> generated when the Protocol-Origin is BGP. It says: >> >> “Protocol-Origin is BGP SR Policy, it is provided by the BGP >> component on the headend and is: >> >> o the BGP Router ID and ASN of the node/controller signalling the >> candidate path when it has a BGP session to the headend, OR >> >> o the BGP Router ID of the eBGP peer signalling the candidate path >> along with ASN of origin when the signalling is done via one or more >> intermediate eBGP routers, OR >> >> o the BGP Originator ID [RFC4456] and the ASN of the >> node/controller when the signalling is done via one or more >> route-reflectors over iBGP session.” >> >> >> >> In the operator's network, in order to reduce the number of BGP sessions >> in controller and achieve scalability, the controller only establishes eBGP >> peer with the RR. And the RR establishes iBGP peers with the headends.. As >> mentioned in the draft, the headend will use the RR's Router ID as the CP's >> node-address (the signaling is done via route transmission from RR to the >> headend instead of route reflection). The headend needs to carry the CP's >> key when reporting the SR Policy status to the controller through BGP-LS. >> And there is a problem that the controller may not recognize the key >> because the node-address is generated by the RR node. >> >> >> >> For network robustness, two or more RRs are usually deployed. This will >> introduce another problem.. When the same CP advertised by the controller >> is delivered to the headend through different RRs, the headend cannot >> distinguish whether it is the same CP because the node-address in the CPs' >> key comes from different RRs. >> >> >> >> To solve these problems, We recommend carrying the Route Origin >> Community (defined in RFC 4360) directly when the controller advertises BGP >> routes. In this way, the key of the CP is determined by the controller >> and will not change during the advertisement of BGP routes. >> >> >> >> Thanks, >> >> Cheng >> >> _______________________________________________ >> Idr mailing list >> Idr@ietf.org >> https://www.ietf.org/mailman/listinfo/idr >> >> _______________________________________________ > spring mailing list > spring@ietf.org > https://www.ietf.org/mailman/listinfo/spring > -- <http://www.verizon.com/> *Gyan Mishra* *Network Solutions A**rchitect * *M 301 502-134713101 Columbia Pike *Silver Spring, MD
- Re: [Idr] Comments: Route Origin Community in SR … Ketan Talaulikar (ketant)
- Re: [Idr] Comments: Route Origin Community in SR … Robert Raszuk
- Re: [Idr] Comments: Route Origin Community in SR … Ketan Talaulikar (ketant)
- [Idr] 答复: Comments: Route Origin Community in SR … Fangsheng
- Re: [Idr] Comments: Route Origin Community in SR … Robert Raszuk
- Re: [Idr] Comments: Route Origin Community in SR … Fangsheng
- Re: [Idr] Comments: Route Origin Community in SR … Ketan Talaulikar (ketant)
- Re: [Idr] Comments: Route Origin Community in SR … Fangsheng
- [Idr] 答复: [spring] Comments: Route Origin Communi… Aijun Wang
- Re: [Idr] Comments: Route Origin Community in SR … Ketan Talaulikar (ketant)
- Re: [Idr] [spring] Comments: Route Origin Communi… Ketan Talaulikar (ketant)
- [Idr] 答复: [spring] Comments: Route Origin Communi… Aijun Wang
- Re: [Idr] [spring] Comments: Route Origin Communi… Ketan Talaulikar (ketant)
- Re: [Idr] [spring] Comments: Route Origin Communi… Gyan Mishra
- Re: [Idr] [spring] Comments: Route Origin Communi… Ketan Talaulikar (ketant)
- Re: [Idr] Comments: Route Origin Community in SR … Ketan Talaulikar (ketant)
- Re: [Idr] [spring] Comments: Route Origin Communi… Gyan Mishra
- Re: [Idr] [spring] Comments: Route Origin Communi… Gyan Mishra
- Re: [Idr] [spring] Comments: Route Origin Communi… Ketan Talaulikar (ketant)
- Re: [Idr] [spring] Comments: Route Origin Communi… Ketan Talaulikar (ketant)
- Re: [Idr] [spring] Comments: Route Origin Communi… Gyan Mishra
- Re: [Idr] Comments: Route Origin Community in SR … Chengli (Cheng Li)